| 钯掺杂α-MnO2无溶剂下催化氧化苯甲醇的性能 |
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| 作者姓名： | 黄秀兵 王静静 郑海燕 路桂隆 王鹏 |
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| 作者单位： | 1.北京科技大学材料科学与工程学院 北京 100083 |
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| 基金项目： | 国家自然科学基金资助项目51802015中央高校基本科研业务费资助项目FRF-TP-16-028A1北京市青年骨干个人项目资助项目2017000020124G090 |
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| 摘 要： | 通过共沉淀和原位煅烧转化方法, 将Pd掺杂δ-MnO2前驱体煅烧后制备得到Pd掺杂α-MnO2纳米棒催化材料.通过氮气物理吸附、X射线衍射、透射电子显微镜、扫描电子显微镜、热重分析、X射线光电子能谱等技术对催化材料进行了表征.扫描电镜和透射电镜结果显示, α-MnO2纳米棒表面没有明显的Pd纳米颗粒, 表明Pd可能掺杂到α-MnO2晶格中.纯α-MnO2的还原温度在390℃左右, 但Pd掺杂可以极大地促进α-MnO2还原, 还原温度可低至约200℃左右.研究了所制备催化剂在无溶剂条件下对于以分子氧为氧化剂选择性催化氧化苯甲醇为苯甲醛的催化性能.结果表明: 在无溶剂及用纯氧气为氧化剂条件下, Pd掺杂α-MnO2纳米棒对苯甲醇氧化显示出增强的催化活性; 所掺杂的氧化态Pd物质可增强催化材料中的氧迁移率; 在这些Pd掺杂α-MnO2催化材料中, 当以Pd (3%, 质量分数) -MnO2为催化剂时, 在110℃反应4 h后, 苯甲醇的转化率为39%, 远高于同条件下以纯α-MnO2为催化剂时18. 3%的苯甲醇转化率.
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| 关 键 词： | 纳米棒 α-MnO2 钯掺杂 无溶剂氧化 溶胶-凝胶制备 |
| 收稿时间： | 2018-09-10 |
Catalytic performance of Pd-doped α-MnO2 for oxidation of benzyl alcohol under solvent-free conditions |
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| Affiliation: | 1.School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China2.Beijing Advanced Innovation Center for Materials Genome Engineering, Beijing 100083, China |
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| Abstract: | Liquid-phase selective oxidation of benzyl alcohol to benzaldehyde is one of the most important processes in both laboratory and chemical industry processes due to the remarkable values of benzaldehyde in the production of flavours, fragrances, and biologically active compounds. In the traditional processes for selective oxidation of benzyl alcohol using a stoichiometric or excessive amount of toxic and expensive inorganic oxidants, such as ammonium permanganate in aqueous acidic medium, a large amount of toxic waste is produced. A few studies on the benzyl alcohol-to-benzaldehyde oxidation by environmentally clean oxidants (O2 or H2O2) in the presence of organic solvents (e. g., toluene, p-xylene, and trifuorotoluene) have been reported; however, the usage of organic solvent is neither economical nor environmental friendly. Even though the solvent-free oxidation of benzyl alcohol to benzaldehyde using tert-butylhydroperoxide (TBHP) as oxidant has been reported, the co-product of tert-butanol from the consumption of TBHP will be left in the reaction solution, necessitating further separation. Therefore, various heterogeneous catalysts have been developed for solvent-free selective oxidation of benzyl alcohol using flowing air or oxygen; however, in most of these systems, the reaction temperature is still high (> 130 ℃) and/or conversion/selectivity is still low. Thus, the development of efficient heterogeneous catalysts for the solvent-free se-lective oxidation of benzyl alcohol with high selectivity and yield using molecular oxygen from air as the oxidant at low temperature is needed. In this study, Pd-doped α-MnO2 nanorods were prepared from Pd-doped δ-MnO2 precursors via a co-precipitation and in situ calcination transformation method. These catalysts were extensively characterized by various techniques, such as N2 adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The SEM and TEM results indicate that there are no obvious Pd nanoparticles on the surface of α-MnO2 nanorods, signifying the possible doping of Pd into the lattice of α-MnO2. The reduction temperature of pureα-MnO2 is around 390 ℃, while the doped Pd could greatly promote α-MnO2 reduction to lower temperatures at around 200 ℃. The applications of Pd-doped α-MnO2 nanorods as catalysts for selective aerobic oxidation of benzyl alcohol to benzaldehyde under solventfree conditions with molecular oxygen were investigated. As compared with pure α-MnO2, the Pd-doped α-MnO2 nanorods show enhanced catalytic activity for selective oxidation of benzyl alcohol under solvent-free conditions with O2, which can be attributed to the beneficial presence of oxidized palladium species and enhanced oxygen mobility resulting from the doping Pd species. In these Pddoped α-MnO2 nanorods, when Pd (3%) -MnO2 was used as catalyst, a 39% conversion of benzyl alcohol was achieved. It is much higher than the 18. 3% conversion when pure α-MnO2 used as catalyst at 110 ℃ and reaction time of 4 h. |
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